The present invention relates to a mechanism for adjusting binoculars to a distance corresponding to a span length between the human eyes. More particularly, the invention relates to an adjustment mechanism for moving both lens barrels of the binoculars in the lateral direction.
As is well known, human eye spans are different according to age, sex, and individual physical characteristics. For this reason, it is necessary to provide an adjustment mechanism on binoculars for adjusting the distance of the two barrels according to the eye span of the user. There has previously been provided an adjusting mechanism in which right and left lens barrels are connected to each other by a screw so that the barrels can be moved nearer or closer to one another by bending the connected portions. However, in this prior art construction, it is very difficult to provide an adjustment for the resistance to movement provided by the screw which connects the right and left lens barrels. The prior art construction is thus disadvantageous in that the barrels are either too hard to move or are too loose to maintain a desired span length.
Moreover, it is impossible to apply such a prior art mechanism to automatic focus detecting-type binoculars as proposed in copending United States patent application Ser. No. 74,354, filed Sept. 10, 1979 by the present applicants since the relationships among the right and left lens barrels and the intermediate connecting parts thereof is variable. In such binoculars incorporating an automatic focus detecting system, it is required that both lens barrels and the control connecting parts be maintained in the horizontal or lateral direction. In automatic detecting binoculars, a focus detecting element module is disposed between the right and left lens barrels in the central connecting portion and the oculars are moved so that the two images through the two lens barrels coincide to thereby implement the focussing operation automatically. In contrast, in the prior art construction in which the position relation among the lens barrels and the connecting portion are varied, it would be impossible for the respective images focussed through both lens barrels to be properly formed on the focus detecting element module.
It is a primary object of the invention to overcome the above-noted defects inherent in the prior art construction. Specifically, it is an object of the invention to provide an automatic eye span adjustment mechanism capable of compatible operation with automatic focussing binoculars.